This is only one research example and the opinion of one result. It has been my experience if you ask one question of two PhD who share the same office. You get 3 answers. They each have their own opinion and a mutual opinion.
Unfortunate this Study doesn't take into account the SPRING BACK EFFECT. True PGR slow down top growth and some lateral growth. However as the PGR wear off the Plant grows extra fast. Thus the SPRING BACK EFFECT. Plus while the PGR is working it creates a thicker stronger plant and that is why there is a boom in growth as the PGR wears off. Therefore proper timing of application and non application of a PGR will decrease grow in time for plugs.